Mycobacterium tuberculosis is a remarkably successful human pathogen, and has coexisted with humans for thousands of years. Although only -10% of infected individuals develop active tuberculosis, the shear number of latently infected persons results in 8 million new cases of TB and 2 million deaths worldwide every year. The immune response to M. tuberculosis proceeds slowly but culminates in a granuloma. This collection of immune cells not only functions to focus the immune response on the area of infected macrophages, but also serves as an immunologic barrier to dissemination of the infection throughout the lungs. Interestingly, a proportion of M. tuberculosis bacilli can survive and persist in the granuloma, and this structure appears to greatly facilitate transmission of disease by causing pathology in the lungs. Thus, the granuloma is the intermediate goal for both the host and the pathogen. This makes identifying the "protective" and "pathologic" features of the immune response to M. tuberculosis complex and difficult. As a collaborative project for the past 14 years, we have studied the signals and factors that result in cell migration and granuloma formation in tuberculosis, with particular attention paid to tumor necrosis factor (TNF). TNF is a master regulator of the granulomatous response and of many aspects of the immune system. Humans treated with TNF neutralizing agents have a substantially increased risk of tuberculosis. We propose to follow up on our previous findings to study aspects of TNF and cell migration in the murine model of tuberculosis. Specifically, we will identify mechanisms the pro- and anti-inflammatory mechanisms related to TNF in M. tuberculosis infection (Aim 1), generate novel inducible knockout strains to determine which cell types are responsible for controlling the various phases of infection (Aim 2), and follow up on surprising findings that the chemokine receptor CXCR3 may impair the ability of the host to control M. tuberculosis infection (Aim 3). Our goal is a better understanding of the interplay between host and pathogen during infection, to identify strategies to eliminate persistent organisms.